1. Field of the Invention
This invention relates to: blood pressure measuring devices and particularly concerns an improved method and apparatus for measuring blood pressure, specifically by modifying a conventional sphygmomanometer to allow the user to more easily and inexpensively conduct the measurement of systolic and diastolic blood pressures.
2. Background and Related Disclosures
The conventional method and apparatus most commonly used for measuring blood pressure in a physician's office involves the use of a sphygmomanometer, which includes an inflatable cuff, a pressure gauge, a bleed valve, a check valve and a hand-held resilient inflation bulb pump to supply air pressure to inflate the cuff, all cooperating in pneumatic communication with one another.
The user wraps and secures the inflatable cuff around the upper arm (or leg) of the patient and inflates the cuff by squeezing the hand-held inflation bulb one or more times until, in the case of an arm, the brachial aderial blood flow is arrested by the inflating cuff. Inflation cuffs come in various sizes, a larger cuff, known as an obese or thigh cuff, is used on individuals with larger arms or on the thigh, respectively.
The cessation of arterial blood flow is usually monitored by using a stethoscope or electronic indicator, held with the other hand and placed over the brachial artery as it passes through the antecubital fossa of the arm. The bleed valve is opened to release pressure while the user listens for the recurrence of aderial blow flow, the auscultatory "Korotkov sound," where a wave of blood is released, which indicates that the patient's own blood pressure has overcome the pressure exerted by the inflatable cuff: this indicates the systolic blood pressure. The user continues to deflate the cuff until the arterial pressure no longer must overcome the pressure of the inflatable cuff, listening for disappearance of the Korotkov sound, which indicates that the blood pressure is no longer working against the air pressure in the inflatable cuff: this indicates diastolic blood pressure.
Blood pressure is usually measured in millimeters of mercury (mmHg.) and expressed as systotic/diastolic. Blood pressure has a normal range of about 100-130 mmHg. for systolic and 60-80 mmHg. for diastolic, with a wide variation depending on the blood pressure of the patient.
The above method is adequate and apparatus have been used for years. However, repetitively squeezing the inflation bulb to inflate the cuff can cause muscle strain and repetitive motion injuries (such as carpal tunnel syndrome in the wrist and/or lateral epicondylitis in the elbow) when the user is taking a large number of blood pressure measurements, or a small number of measurements each day over time. In addition, it is sometimes necessary to use the larger inflatable obese cuff on obese patients, requiring many more squeezes of the hand-held inflation bulb, exacerbating the above-described problem of muscle strain.
The above method and apparatus also requires that the user rather awkwardly hold and manipulate instruments in either hand, the bulb/bleed valve in one and the stethoscope in the other.
Attempts in the past to overcome the problem have required expensive and cumbersome electrical equipment and motors, which further require a source of electricity and likely returns a less accurate measurement than the conventional method. Air pumps powered by an electrical motor have been used in the past to inflate the cuff but a certain, sometimes critical, amount of accuracy is sacrificed for the convenience of this apparatus. Typically the user has insufficient control over the inflation and/or deflation rates of the cuff when using an electric air pump, being limited to turning the electric pump on or off. Should the patient have a slow pulse rate, the cuff pressure can climb or fall significantly between pulses. Systolic and diastolic blood pressures are measured by the occurrence and cessation of the pulse and, should the air pressure of the cuff climb or fall rapidly between two pulses, the resulting readings will reflect incorrect pressures.
Manually powered pumps: such as inflation bulbs, allow the user to control the flow of air much more closely because the user must himself supply the physical work for every millibar of pressure and so can regulate the amount and rate of air delivery with great accuracy.
Two factors must be balanced when determining a good air pump volume to be used with a given inflatable cuff. If too many squeezes are required to inflate the cuff then the user will become fatigued and vulnerable to the repetitive motion injuries discussed above. If too few squeezes are required to inflate the cuff then the user is delivering a relatively large volume of air witch each squeeze or stroke and hence fine control of the volume of air delivered is diminished.